To help spell a word, you can usually use the NATO Phonetic Alphabet.
In Germany unfortunately they use a different set of words. A is Anton and not Alpha, B is Berta and not Bravo.
It is sometimes difficult to be sure whether someone said M or N, and in German you can sometimes hear E and I wrong, especially if it spoken by an English speaking person.

Below is a table with the German terms. To spell Melktert to a German person, you will say: M wie Martha, E wie Emil, L wie Ludwig, K wie Kaufmann, T wie Theodor, E wie Emil, R wie Richard and T wie Theodor